Sealing arrangement and sealing method

ABSTRACT

The invention relates to a sealing arrangement ( 100 ) for sealing a leak ( 21 ) in a casing ( 2 ) or for sealing off a production zone ( 1 ) where the casing having a circumference and perforations ( 3 ) is situated in a borehole ( 22 ) downhole, but with a distance to an inner wall of the borehole, creating an intervening space ( 4 ) there between. The sealing arrangement comprises a composition ( 5 ) for injection into the intervening space or into a leak in the casing, and a non-miscible net comprised in the composition after injection in order to fixate the injected composition in a predetermined position.

TECHNICAL FIELD

The present invention relates to a sealing arrangement for sealing a leak in a casing or for sealing off a production zone where the casing having a circumference and perforations is situated in a borehole downhole, but with a distance to an inner wall of the borehole, creating an intervening space there between. Furthermore, the invention relates to a sealing method.

BACKGROUND

Casings are placed in boreholes in the formation mainly for preventing a collapse of the boreholes. The borehole may have a number of casings situated within another so that a production casing is partly situated within an intermediate casing which again is situated within a surface casing and a conductor pipe. The conductor pipe is cemented to the formation, and the surface casing and the intermediate casing are cemented within the conductor pipe.

In some cases, the production casing is fixed within the intermediate casing by means of packers leaving an open space between the production casing and the intermediate casing. When producing oil, as a safety precaution, the internal pressure in the open space and the production casing, respectively, must not differ too much from each other. If the pressure difference is too high, it may be necessary to minimise the space by inserting a packer closer to the surface. Inserting a packer at this stage can, however, be a difficult operation.

After the production casing has been placed in the borehole, it is subsequently perforated in a certain zone where oil is present, a so-called production zone. Then, the oil fluid is able to enter into the production casing and oil production is initiated. During the oil production phase, the oil fluid may be emulsified with water as the zone with oil may shift when emptying the oil reservoir for oil.

In the event that the zone with oil has shifted, it is necessary to make new perforations in the production casing and to seal off the previous perforations. In order to seal off the previous perforations, a new production casing is inserted within the previous production casing and packers are placed on both sides of the zone. Subsequently, new perforations are made in the new production casing.

By inserting a new production casing into the previous production casing, the production rate is substantially diminished due to the increase in friction and the velocity is likewise decreased causing a variety of related problems.

Another way to seal off the zone with water is to insert a cement plug above the zone for plugging the underlying casing. Subsequently, the production casing is perforated in a new area above the cement plug where oil is present. Hereby, the underlying casing is shut off more permanently and it is very difficult, if not impossible, to resume the production in the production casing beneath the plug without having to insert a new production casing.

Another way is disclosed in U.S. Pat. No. 3,967,681 in which gellable polymer is ejected prior to the cement so that the gellable polymer is allowed to gel in order to slow the borehole fluid down and hinder the borehole fluid from forcing the subsequent cement away from the position in which it needs to harden. This method requires a first step of inserting a retainer below the perforations and a second step of inserting a packer above the perforations to be sealed off, both of which steps are difficult, complicated, and expensive.

In another situation, the production casing has a leak which needs to be sealed. A known solution is to expand a liner from within the production casing resulting in a somewhat uneven surface inside the casing, influencing the flow of the oil.

DESCRIPTION OF THE INVENTION

An aspect of the present invention is, at least partly, to overcome the disadvantages of the known solution to sealing off a leak, perforations, or a production zone or minimising the open space between the production casing and the intermediate casing.

As will become evident from the description below, an improved solution is thus suggested, which may be obtained by a sealing arrangement for sealing a leak in a casing or for sealing off a production zone where the casing having a circumference and perforations is situated in a borehole downhole, but with a distance to an inner wall of the borehole, creating an intervening space there between, comprising:

-   -   a composition for injection into the intervening space or into a         leak in the casing, and     -   a non-miscible net comprised in the composition after injection         in order to fixate the injected composition in a predetermined         position.

The net may be a mesh, a woven wire, a wire netting, a netting, a web, a grid, a lattice, or a grating.

In one embodiment, the net may be ejected prior to or simultaneously with the composition.

Moreover, the net may be ejected prior to or simultaneously with the composition as elongated components, such as strings or threads forming the mesh, woven wire, wire netting, web, grid, lattice, or grating after ejection.

The net may be made of wire, coiled wire, polymer thread, polymer fibre, carbon fibre, glass fibre, metal threads, or a like elongated component.

In another embodiment, the net may be made of a magnetic material.

The net may be made of elements in the composition pasting together and thereby forming a netting or a net within the composition.

Moreover, each element may be made of a magnetic material.

In one embodiment, the net may be made of elements in the composition pasting together and thereby forming a netting or a net within the composition.

In addition, each element may be made of a magnetic material.

The invention also relates to a sealing arrangement for sealing a leak in a casing or for sealing off a production zone where the casing having a circumference and perforations is situated in a borehole downhole, but with a distance to an inner wall of the borehole, creating an intervening space there between, comprising:

-   -   a composition for injection into the intervening space or into a         leak in the casing, and     -   units in the composition pasting together during hardening of         the injected composition and thereby forming a netting or a net         within the composition, wherein each of the units have a core         enclosed within a compound.

In one embodiment, each separate unit may have an intermediate substance between the core and the surrounding compound.

Moreover, the core or the intermediate substance may be made from ceramics, metal, polymer fibre, glass fibre, or a magnetic material making the separate units paste together.

The composition may comprise a compound.

In one embodiment, the compound may comprise cement, polymer, synthetic rubber, natural rubber, or silicone.

In addition, the compound may comprise a curing agent, binding agent, hardener, or accelerator.

The invention also relates to a sealing method for sealing a leak or a production zone or for minimising an open space above a packer between a production casing and an intermediate casing, comprising the steps of:

-   -   injecting a compound,     -   forming of a non-miscible net in the compound in order to fixate         the injected compound in a predetermined position.

In one embodiment, the net may be discharged prior to or simultaneously with the injecting step and take form within the compound when the compound is injected to at least partly surround the net.

In another embodiment, the net may be formed from elements or units pasting together within the composition during hardening or stiffening of the compound or the composition.

Finally, the invention also relates to a downhole tool comprising a chamber comprising a sealing arrangement as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail below with reference to the drawings, in which

FIG. 1 shows a sectional view into the borehole with a production casing, intermediate casings, surface casing, and conductor pipe,

FIG. 2 shows a sectional view into a borehole where a casing having a leak is situated within the borehole,

FIG. 3 shows a partially sectional view of a perforated casing where each perforation has been sealed with a sealing arrangement,

FIG. 4 shows a sectional view of a blocked casing,

FIG. 5 shows a sectional view of the casing of FIG. 2 with a sealing arrangement comprising coiled wires for sealing the leak,

FIG. 6 shows a sectional view of the casing of FIG. 2 with an embodiment of the sealing arrangement comprising pasting beads or balls,

FIG. 7 shows a sectional view of the casing of FIG. 2 with another embodiment of the sealing arrangement comprising fibres,

FIG. 8 shows a sectional view of the casing of FIG. 2 with yet another embodiment of the sealing arrangement comprising a lattice, and

FIG. 9 shows a cross-sectional view of composition comprised of separate elements.

The drawings are merely schematic and shown for an illustrative purpose.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a sealing arrangement 100 comprising a composition 5 and a non-miscible net 30 for fixating the composition 5 in a predetermined position while the composition 5 fastens to its surroundings. Typically, the composition 5 is injected into a well comprising a highly pressurised fluid and thus, the net is needed to dam this pressurised fluid so that the composition has time to harden.

The composition can be in the form of a compound or in the form of separate units.

When the composition 5 is in form of a compound, the compound is injected in its liquid phase, and while the compound hardens it needs to be held in place in a certain position, which is accomplished by the net 30. Thus, the net serves to hinder the compound from being flushed away from the leak.

In one embodiment, the composition 5 is melted before being injected and hardens/stiffens when injected. In another embodiment, the composition 5 consists of one base part in its liquid form, or at least in a partly liquid form, which is mixed with another part such as a hardener prior to being injected in order to make the compound harden. By a partly liquid form is meant an injectable base part which is partly liquid and partly solid.

In another embodiment, the composition 5 expands or swells while hardening. The composition 5 may be any kind of expandable or swellable composition. The composition may thus be a two-part glue where the parts when mixed expand and harden. In another embodiment, the composition 5 expands when subjected to the oil fluid containing water seeping from the formation and/or when subjected to the heat of the fluid. Additionally, the composition 5 may be of the type which does not expand, but only hardens when subjected to the oil fluid containing water or the heat of the fluid seeping from the formation. Here the oil fluid is an emulsion comprising oil and water. Thus, the composition 5 may be a two-part polyurethane glue, or another suitable polymer able to harden in one of the ways mentioned above.

Furthermore, the composition 5 may comprise a resin and a catalyst reacting under pressure whereby the composition hardens. Thus, the composition 5 reacts when exposed to a certain pressure which may be applied by the injection tool 13 just before injecting the composition. Alternatively, the reaction may come from the high pressure within the borehole 22 when the composition has been injected.

In another embodiment, the composition comprises separate units in the form of balls, beads, or the like objects. Each unit has an external layer of a compound enabling the units to paste together after injection and thereby form a net, as shown in FIG. 9.

A sealing arrangement 1 according to the present invention can be used in a variety of situations. One such situation is where a production casing 2 is held in place within an intermediate casing 20 by means of a packer 19, and where the pressure in the open space 23 above the packer 19 is too different from the pressure within the production casing 2 to satisfy safety regulations. In such events, it is necessary to minimise the open space by placing an obstruction in form of a sealing arrangement 100 above the packer 19 as shown in FIG. 1.

Another situation is shown in FIG. 2, in which a leak 21 has occurred in a casing 2 downhole. The casing 2 is placed in a borehole 22 and an intervening space 4 is thus created between the outside wall of the casing and the inside of the borehole. In such a situation, the sealing arrangement 100 is inserted into this cavity 24 outside the leak 21, the composition 5 being injected both into and through the leak in order to seal the leak in the casing.

The sealing arrangement 100 can also be used in a situation where a perforated casing 2 is used in a borehole 22 and an oil production zone 1 for some reason has shifted or oil is no longer present in that zone. Perforations 3 are provided outside the production zone 1 enabling oil to flow into the casing 2 and in this way be brought up from downhole. When oil is sufficiently mixed with water or the reservoir has become emptied of oil, the perforations 3 of the casing 2 need to be sealed so that a new production zone can made in another place along the casing string. Thus, the sealing arrangement 100 may be used for closing a perforated zone in a casing 2 as shown in FIG. 3. In this case, the sealing arrangement 100 is placed in the intervening space 4 between the outside of the casing 2 and the inside of the borehole 22. The sealing arrangement 100 only needs to cover the perforations as a bead is fastened inside each perforation, projecting somewhat outwards radially from the casing. Thus, the sealing arrangement 100 needs not fill the whole intervening space 4 in order to close the perforations 3.

Additionally, the sealing arrangement 100 can be used to block the lowest part of the well by blocking the casing 2 from within and across its entire internal area as shown in FIG. 4. Since the sealing arrangement 100 comprises a net 30, the blocking of the casing 2 can be performed at every level of the casing and not just at the bottom by filling up the casing from the bottom.

The sealing arrangement 100 may comprise a composition 5 which is in its liquid or partially liquid phase when injected. In this embodiment, the net 30 is a plurality of interlacing lines 29 in the form of a woven wire, a wire netting, a web, a grid, a lattice 27, a grating, or the like nets. The net 30 is compressed during storage in the injection tool 13 and is discharged either before the composition 5 or simultaneously with the composition.

In FIG. 5, the net 30 is made of coiled metal wires 28 or threads which are compressed in the tool 13 by stacking the windings of each coiled wire 28 onto each other forming a coil or a helically spring. The net 30 can also be made of wire, core, polymer thread, glass fibre threads, or a like elongated component being tangled up into a net during injection.

In another embodiment, the net 30 is an expandable lattice 27 as shown in FIG. 8, in which first interlacing lines 29 cross second interlacing lines 29, the interlacing lines being twisted so that each first interlacing lines abut other adjacent first interlacing lines and each second interlacing lines abut other adjacent second interlacing lines. Thus, the compressed lattice 27 has the form of an elongated member and the expanded lattice has the form of a sheet. In yet another embodiment, the net 30 is in the form of a grid made of a slit plate which, when expanded, forms a perforated plate. Such nets 30 can be discharged prior to the injection of the composition 5 in order to retain the composition and form the sealing arrangement 100.

The elements forming the net 30 can also be comprised in the composition 5 and be formed during hardening of the composition. In this case, the net 30 is formed from elements pasting together during hardening of the injected composition 5. The elements may be in the form of beads or small balls 25 as shown in FIG. 6, or in the form of fibres 36 or threads as shown in FIG. 7. The elements may be made from a magnetic material and the net is formed as the composition is injected and the elements injected first fasten themselves to the casing, thus building a net projecting out from the casing.

The net may be made from wire, coiled wire (28), polymer thread, polymer fibre, carbon fibre, glass fibre, metal threads, or a like elongated component

In FIGS. 2, 5, 6 and 7, the composition 5 is injected so that it hits the inside wall of the borehole 22. In order to hold the composition 5 in position outside the leak 21 in the casing 2, a net 30 is discharged together with the composition. As mentioned above, the net 30 shown in FIG. 5 can also be discharged prior to the injection of the composition 5. The net 30 helps the composition bridge he gap between the outside of the leak in the casing 2 and the inside wall of the borehole 22.

In some embodiments, the composition 5 is a compound comprising cement, polymer, synthetic rubber, natural rubber, and/or silicone. When using rubber or silicone, the compound is typically melted prior to the injection. The melting process is performed in the injection tool 13 or prior to loading the compound into the tool.

The polymer may be any suitable elastomer or a thermoplastic polymer. The elastomer may comprise nitrile rubber (NBR), hydrogenated nitrile rubber (HNBR), carboxyl nitrile rubber (XNBR), silicone rubber, ethylene-propylene-diene copolymer (EPDM), fluoroelastomer (FKM, FEPM), and perfluoroelastomer (FFKM), or other suitable polymers. Thermoplastic polymer may comprise Teflon, polyetheretherketone, polypropylene, polystyrene, and polyphenylene sulphide, or other suitable polymers.

In order to absorb water from the emulsified fluid seeping from the formation, the polymer may comprise any water-soluble polymer able to absorb water, thus enabling a hardening of the compound. Such water-soluble polymer may be methylcellulose, cellulose acetate phthalate, and hydroxypropyl methylcellulose polymers, poly (ethylene oxide) polymers, guar and its derivatives, polyacrylamide, polyvinylpyrolidone, polyacrylic acid, polyvinylpyrolidone, oligo maleinate copolymers, oligo maleinate oligomers, allyl maleate oligomers, silicon-based materials, and flouro-silicone based materials.

As mentioned, the compound can comprise a hardener or a curing agent when the compound is stored in a two-part form and mixed just before injection of the compound. In order for the elements to paste together, the compound may comprise a binding agent. The binding agent can also be added to the composition 5 in order for the compound to bind to the metal wire or other elongated components. The process of stiffening or hardening must take place immediately after the composition 5 has been injected so that the highly pressurised fluid in the well does not interfere with the forming of a sealing arrangement 100 in a predetermined position, and the compound may therefore be provided with an accelerator.

When using a net 30 of metal—such as coiled wire 28, threads, woven wire, wire netting, a web, a grid, a lattice 27, or a grating—the net can be used to provide heat to the compound thereby accelerating the hardening process. Electricity is led through the metal and transformed into heat, which again is ejected into the compound from within the compound.

As mentioned, the composition 5 may comprise a plurality of separate units each having a core enclosed by a compound. The compound may be the same as mentioned above and enable the units to paste together after being ejected into the intervening space. Thus, the net is made from the separate units pasting together during hardening of the compound and thereby forming the net.

In FIG. 9, the composition comprises a plurality of separate units. Each unit has a core 31 enclosed within an intermediate substance 32 which again is enclosed within an external layer 33 of compound. When ejecting the units into the intervening space to make a circumferential seal, the units paste together as a seal in that the compound layer of one unit pastes to the compound layer of another unit. In this embodiment, the compound becomes sticky when reacting with the water in the intervening space.

In one embodiment, the elements, the core, or the intermediate substance are made from ceramics, metal, polymer, glass fibre, cellulose, or pulpwood.

In another embodiment, the core of each separate unit is made of a magnetic material making the separate units paste together. Thus, the units will be drawn towards one another when injected and, since the casing through which the composition is injected is of metal, the units will also stick to the casing. In this way, a leak is easily sealed without filling up the whole intervening space.

Each element has an extension of at least 0.1 mm in one direction.

A net is a physical network comprised in the compound or composition as a separate part or parts. The net may also be formed in the composition as separate units pasting together as a network of units connecting to each other.

A non-miscible net is a net made of a material which is non-miscible with the compound or the composition. Hereby, the net is formed in the composition or the compound without making a chemical bond with the composition or the compound. Thus, the net is formed as a separate net in the composition or the compound.

In FIG. 3, the closing of the perforations 3 of the casing 2 is shown in form of projections projecting radially outwards from each perforation; however, the closing can also be made as circumferential seals. The circumferential seals are made by injecting composition 5 into several perforations 3 and into the intervening space 4 around the outside of the casing 2. Each seal is made by injecting the composition 5 through holes situated along an intersecting line where a plane extending perpendicular to the longitudinal extension of the casing 2 intersects with the circumference of the casing. Thus, the circumferential seal has an extension around the outside of the casing 2 substantially perpendicular to the extension of the casing. The perforations 3 through which the composition 5 has been injected may be filled with composition during the expansion process of the composition.

The injection of composition 5 is performed by an injection tool 13 as shown in FIG. 2. The injection tool 13 is submerged into the casing 2, and an injection tip 16 is subsequently moved outwards in a radial direction of the casing through and outside some of the perforations 3 or the leak 21.

Furthermore, the perforations 3 or the leak 21 may be too small for the injection tip 16 to inject the composition into the intervening space. In this event, the perforations 3 or the leak 21 must be widened before the injection step can take place. This is performed by a drilling tool.

The injection tool 13 has at least one chamber comprising the composition 5 to be injected. In one embodiment, the tool 13 has one chamber of composition and, in another embodiment, the tool may have several chambers each comprising enough composition to make one circumferential seal. Due to the fact that the composition 5 expands subsequent to being injected into the intervening space 4, the chamber does not need to be of the same volume as the final seal or seals.

In one embodiment, the injection tool 13 may be part of a system which also comprises a drilling tool able to expand the perforations 3 or drill holes in the casing 2 prior to the injection steps. The drilling tool may also be a separate tool which is submerged into the casing 2 prior to the injection tool 13 so that the drilling operation and the injection operation is performed in two separate runs.

In the event that the tools are not submergible all the way into the casing, a downhole tractor can be used to push the tools all the way into position in the well. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®. 

1. Sealing arrangement (100) for sealing a leak (21) in a casing (2) or for sealing off a production zone (1) where the casing having a circumference and perforations (3) is situated in a borehole (22) downhole, but with a distance to an inner wall of the borehole, creating an intervening space (4) there between, comprising: a composition (5) for injection into the intervening space or into a leak in the casing, and a non-miscible net comprised in the composition after injection in order to fixate the injected composition in a predetermined position.
 2. Sealing arrangement according to claim 1, wherein the net is a mesh, a woven wire, a wire netting, a netting, a web, a grid, a lattice, or a grating.
 3. Sealing arrangement according to claim 1, wherein the net is ejected prior to or simultaneously with the composition.
 4. Sealing arrangement according to claim 1, wherein the net is ejected prior to or simultaneously with the composition as elongated components, such as strings or threads forming the mesh, woven wire, wire netting, web, grid, lattice, or grating after ejection.
 5. Sealing arrangement according to claim 1, wherein the net is made of wire, coiled wire (28), polymer thread, polymer fibre, carbon fibre, glass fibre, metal threads, or a like elongated component.
 6. Sealing arrangement according to claim 1, wherein the net is made of a magnetic material.
 7. Sealing arrangement according to claim 1, wherein the net is made of elements in the composition pasting together and thereby forming a netting or a net within the composition.
 8. Sealing arrangement according to claim 7, wherein each element is made of a magnetic material.
 9. Sealing arrangement (100) for sealing a leak (21) in a casing (2) or for sealing off a production zone (1) where the casing having a circumference and perforations (3) is situated in a borehole (22) downhole, but with a distance to an inner wall of the borehole, creating an intervening space (4) there between, comprising: a composition (5) for injection into the intervening space or into a leak in the casing, and units in the composition pasting together during hardening of the injected composition and thereby forming a netting or a net within the composition, wherein each of the units have a core enclosed within a compound.
 10. Sealing arrangement according to claim 9, wherein each separate unit has an intermediate substance between the core and the surrounding compound.
 11. Sealing arrangement according to claim 9, wherein the core or the intermediate substance is made from ceramics, metal, polymer fibre, glass fibre, or a magnetic material making the separate units paste together.
 12. Sealing arrangement according to claim 1, wherein the composition comprises a compound.
 13. Sealing arrangement according to claim 9, wherein the compound comprises cement, polymer, synthetic rubber, natural rubber, or silicone.
 14. Sealing arrangement according to claim 9, wherein the compound comprises a curing agent, binding agent, hardener, or accelerator.
 15. Sealing method for sealing a leak or a production zone or for minimising an open space above a packer (19) between a production casing and an intermediate casing, comprising the steps of: injecting a composition (5), forming of a non-miscible net (30) in the composition in order to fixate the injected composition in a predetermined position.
 16. Sealing method according to claim 15, wherein the net is discharged prior to or simultaneously with the injecting step and takes form within the composition when the composition is injected to at least partly surround the net.
 17. Sealing method according to claim 15, wherein the net is formed from elements or units pasting together within the composition during hardening or stiffening of the compound or the composition.
 18. Downhole tool comprising a chamber comprising the sealing arrangement according to claim
 1. 